As is known to a worker skilled in the art, combustion is a rapid chemical reaction combining fuel components with air resulting in reaction by-products together with heat and light. In order for a proper reaction to occur the fuel to air ratio should be within a predetermined level and this level is directly dependent on the type of fuel being combusted. For example, when this ratio is defined in terms of the mass of air to the mass of fuel, the amount of air required for the combustion of natural gas is greater than that required for coal.
Central heating systems employing a hot fluid circulating through a network of pipes have been used for many years for room space heating, snow melting, indirect swimming pool heating, ground heating and other similar purposes. Such systems are now generically referred to as hydronic heating systems.
One of the biggest problems with hydronic heating systems is combustion efficiency. In environments where temperatures change significantly, the fuel to air ratio can deviate significantly from an optimum predetermined ratio. Poor combustion efficiency can result in greater fuel usage and incomplete combustion, wherein incomplete combustion can produce soot. The potential build-up of soot can become a problem for boiler systems, particularly those that are oil fired. Soot that accumulates on the walls of the heat transfer surfaces significantly reduces the efficiency of the boiler since it can impede heat transfer. For this reason the conventionally known oil fired boilers require frequent cleaning in order to maintain peak operating efficiency.
One of the most effective ways to achieve improved combustion efficiency is to preheat the combustion reactants used by the burner. It is well known that preheating fuel improves the efficiency and cleanliness of the burning process. It has been found that by preheating the fuel before it is burned, the viscosity and other properties of the fuel are affected so that the burner utilises less fuel to provide the same amount of heat energy.
Fuel preheaters of the prior art often have an external power source such as electricity to power an electric heater to heat the fuel before it is passed to the burner nozzle. Other prior art systems pass the fuel in pipes through tanks which contain heated water directed from the boiler to increase the temperature of the fuel before it enters the fuel burner for combustion. U.S. Pat. Nos. 5,109,807, 4,390,007, 4,719,877, 5,221,043 describe the various fuel preheaters.
It is also known that preheating of combustion air going to the burner is another way to improve efficiency and productivity. Similar to preheating fuel, the preheating of combustion air can result in more heat from a given amount of fuel.
In general, combustion air preheaters for fuel burners and like systems utilise combustion exhaust gas heat to preheat combustion air before being introduced to the burner. U.S. Pat. Nos. 4,664,096, 4,751,913, 4,369,029, 4,015,932 and Canadian Patent No. 2,233,053 describe various combustion air preheaters using exhaust gas. While these examples provide a means for preheating combustion air, they do not provide a means for preheating combustion air during cold starts. During cold start operations, hot combustion gases are not yet available and thus preheating of combustion air therewith is not possible.
Further combustion air preheating systems are known, with various improvements, such as that disclosed in U.S. Pat. No. 4,369,029. The system disclosed therein describes a ceramic recuperator for the heating of combustion air. The recuperator is provided with means, especially electrically operated, for heating the ceramic body so that initial combustion air can be heated before firing of the burner and further heating of the recuperator by combustion products. In light of the foregoing, there is a need for a system enabling the control of the combustion environment thereby adjusting the affect of ambient temperatures on the combustion quality in all modes of operation.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.